The present disclosure relates to processes for recovering iodine from an aqueous solution, such as brine. Several different aspects and embodiments are described. Such processes are particularly helpful in extracting iodine while minimizing the safety and disposal problems associated with other processes.
Iodine and its compounds are useful in many applications, including medicine, photography, catalysts, bactericides, disinfectants, pharmaceuticals, fungicides, and dyes. Iodine is a rare element and is mainly produced outside the United States, so the U.S. is a major net importer of iodine. Elemental iodine or diatomic iodine (I2) has a brown/purple color and is commercially valuable, but does not generally exist in its free state in nature. Instead, iodine exists as ions in various oxidation states, such as iodide (I1−).
Iodine ions typically do not occur in a high enough concentration to make recovering elemental iodine economically feasible from conventional sources such as seawater. However, natural brines, i.e. salt solutions associated with petroleum deposits and underground water, typically contain about 100 ppm of iodine, which is about 2,000 times higher than the concentration of iodine in regular seawater. Hence, natural brine has become a commercially viable source for iodine extraction.
In this regard, a major source of iodine today is brine produced as a byproduct of natural gas extraction. Typically, a mixture comprising brine and natural gas is obtained from a natural gas well. The iodine exists in various oxidation states, e.g. −1, +1, +5, and +7. Most of the iodine is in the form of iodide ions (I1−) which are white in color. When one electron is pulled off of the iodide ions, elemental iodine is formed.
Some processes for extracting iodine from aqueous solutions are known. The “blow-out” process is a conventional process using air, gas, and heat. Initially, chlorine (Cl2) is mixed with the brine, causing oxidation and resulting in the formation of elemental iodine and hydrochloric acid. The I2 is extracted from the brine using a counter-current air stream, and then separated out and recovered. However, the “blow-out” process results in large quantities of an acidified solution having a low pH, typically from 1 to 3. Such low pH levels pose serious safety risks and create disposal problems. A base, such as sodium hydroxide, must be introduced to neutralize the acidified brine solution before it may be released into the environment.
Additional processes for extracting iodine from an aqueous solution, such as brine, which do not require lowering the pH of the brine to the levels of the processes discussed above, are desirable.